Regenerator

ABSTRACT

Regenerator vessel provided with means to supply catalyst particles, means to supply an oxygenate gas, means to discharge regenerated catalyst, means to discharge combustion gases from the vessel and means to separate entrained catalyst from the combustion gases, which vessel also comprises, in use, a fluidised bed zone of catalyst at its lower end, wherein in the fluidised bed zone a vertically extending partition, which partition is provided with one or more openings, is present dividing the fluidised bed zone in a dense phase fluidised bed zone and a fast-fluidised bed zone, the dense phase fluidised bed zone provided with the means to supply catalysts and the fast-fluidised bed zone provided with the means to supply an oxygenate gas at its lower end.

[0001] The invention is related to an improved regenerator vessel. Theregenerator vessel can be suitably used in a fluidised catalyticcracking (FCC) process. The regenerator vessel is provided with means tosupply catalyst particles, means to supply an oxygenate gas, means todischarge regenerated catalyst, means to discharge combustion gases fromthe vessel and means to separate entrained catalyst from the combustiongases, which vessel also comprises, in use, a fluidised bed zone ofcatalyst at its lower end.

[0002] Such regenerator vessels are for example described in U.S. Pat.No. 4,435,282. This publication describes a vessel comprising at itslower end a bubbling fluidised bed of catalyst in which the combustionof coke present on the catalysts to be regenerated takes place.

[0003] A disadvantage of the bubbling bed regenerator as described inU.S. Pat. No. 4,435,282 is that they are troubled with stagnant beds,due to poor catalyst flow patterns, and regeneration gas bypassing, dueto the formation of large bubbles within the bubbling dense bed.

[0004] An alternative to the bubbling bed regenerator is the so-called“High Efficiency Regenerator” (HER) design as described in EP-A-610186.The regeneration is performed in a fast-fluidised bed for most of thecoke combustion and a dilute phase transport riser for some COcombustion. Regenerated catalyst is collected in a bubbling dense bedfor reuse and for recycle to the coke combustor. The regeneration ofcatalysts is more efficient than in the bubbling bed regenerator. As aresult the catalyst inventory required in a FCC unit having such aregenerator can be smaller than the inventory of a FCC unit having abubbling bed regenerator This is advantageous, for example because sucha FCC unit can refresh or change its catalyst inventory in a moreefficient manner.

[0005] A disadvantage of the “High Efficiency Regenerator” (HER) designas for example described in EP-A-610186 is their mechanical andoperational complexity. For example the regenerator vessel consists oftwo stacked vessels comprising three different fluidised bed regimes.

[0006] GB-A-769818 discloses a vessel, wherein both stripping andregeneration is performed. Catalyst from the FCC reactor is supplied toan inner vessel zone wherein catalyst is stripped to obtained spentcatalyst. The spent catalyst can flow via openings from inner vesselspace to the outer vessel space. In the latter space regeneration takesplace.

[0007] U.S. Pat. No. 5,198,397 describes a regenerator wherein the spentcatalyst is directly introduced in a fast-fluidised bed zone locatedcentrally in a regenerator vessel. The required temperature forachieving a sufficient combustion of the coke from the catalyst isachieved by mixing the spent catalyst with part of the regeneratedcatalyst at the catalyst inlet. The partly regenerated catalyst thenflows to a second fluidised bed located in the annular space between thecentrally located fast-fluidised bed zone and the regenerator vesselwall. Disclosed is a regeneration process wherein partial combustiontakes place in the fast-fluidised bed and total combustion takes placein the second fluidised bed. In order to avoid after burning in theupper part of the regenerator vessel, when the effluent gasses of bothfluidisation zones meet, a special cyclone arrangement is proposed.

[0008] The present invention is directed to a more simple design for theHigh Efficiency Regenerator than the stacked vessels of the prior artdesign.

[0009] This object is achieved by the following apparatus.

[0010] Regenerator vessel provided with means to supply catalystparticles, means to supply an oxygenate gas, means to dischargeregenerated catalyst, means to discharge combustion gases from thevessel and means to separate entrained catalyst from the combustiongases, which vessel also comprises, in use, a fluidised bed zone ofcatalyst at its lower end, wherein in the fluidised bed zone avertically extending partition, which partition is provided with one ormore openings, is present dividing the fluidised bed zone in a densephase fluidised bed zone and a fast-fluidised bed zone, the dense phasefluidised bed zone provided with the means to supply catalysts and thefast-fluidised bed zone provided with the means to supply an oxygenategas at its lower end.

[0011] The regenerator vessel according the invention provides a simpleone vessel design. In use a fast-fluidised bed is present in onefluidised bed zone resulting in an efficient combustion of the coke. Thetotal catalyst inventory of the regenerator according the invention willbe significantly smaller when compared with a conventional bubbling bedregenerator having the same vessel volume. This is because the densityin the fast-fluidised bed zone will be much smaller than in aconventional bubbling bed regenerator and because the bed level in thedense fluidised bed can be maintained at a lower level than the bedlevel of the bubbling bed regenerator. A further advantage is thatexisting bubbling bed regenerators can be easily modified to theregenerator vessel according to the present invention, for example byproviding the existing vessel with the necessary means to supplyoxygenate gas and a partition to create the two fluidised bed zones.Existing cyclone arrangements of the existing regenerator canadvantageously also be used in the regenerator according to thisinvention. This latter aspect of the invention is especiallyadvantageous regarding the fact that the vast majority of the currentlyexisting FCC units are equipped with a regenerator operating in thebubbling bed mode combined with a general need to operate a FCC unitwith a lower catalyst inventory.

[0012] With fast-fluidised bed zone is especially meant a fluidised bedhaving a catalyst density of between 50 and 400 kg/m³, and preferablylower than 300 kg/m³. The superficial gas velocity is typically higherthan 1.5 m/s and more preferably between 2 and 6 m/s. The gas fractionin the fast-fluidised bed zone will suitably flow upwards withoutsignificant backmixing resulting in an efficient combustion of the cokefrom the catalyst. In contrast the catalyst particles to be regeneratedwill flow upwards with a considerable backmixing in the fast-fluidisedbed zone.

[0013] With dense phase fluidised bed zone is especially meant afluidised bed having a catalyst density of between 300 and 900 kg/m³.The density of the dense phase fluidised bed zone is always higher thanthe density of the fast-fluidised bed zone. More preferably thesuperficial gas velocity is less than 0.3 m/s and more preferablybetween 0.01 and 0.1 m/s. By operating the dense phase fluidised bedzone at such low gas velocities less deactivation of the catalyst willtake place in said zone because of the lower temperature level and lowersteam partial pressure. Due to the low gas velocity and lowertemperature in this zone only a small part of the coke combustion willtake place in this zone. In essence the dense fluidisation zone will actas a storage vessel rather than a regeneration zone. Thus the time atwhich the catalyst is subjected to the more rigorous deactivationconditions, i.e. as in the fast-fluidised bed zone, is reduced whencompared to the state of the art bubbling bed regenerator. Moreover, theproblems with two different effluent gasses as described in U.S. Pat.No. 5,198,397 are also not to be expected. For this reason nomodifications of the existing cyclone arrangement will be required.

[0014] Part of the catalyst will be entrained from the fast-fluidisedbed zone to the upper end of the regenerator vessel. These catalystparticles will be separated from the gases leaving the regeneratorvessel in the separation means. These separation means are suitablystate of the art cyclone separators, comprising primary cyclones andsecondary cyclone. The secondary cyclones further separate catalystparticles from the gaseous effluent of the primary cyclones. See alsofor example “Fluid Catalytic Cracking Technology and Operations”, JosephW. Wilson, Penn Well Books, Tulsa, 1997, pages 183-185.

[0015] In one preferred embodiment of the invention the means todischarge regenerated catalysts from the regenerator will be positionedat the lower end of the fast-fluidised bed zone. The catalyst particleswhich have been regenerated in the fast-fluidised bed mode will bereturned to this bed from the upper end of the regenerator vessel viafor example the diplegs of the primary and secondary cyclones. Thesereturned catalyst particles will flow mainly downwards in thefast-fluidised bed zone to be discharged from the regenerator vessel inthe lower end thereof. If the openings in the partition are locatedrelatively near to the lower end of the vessel and thus near to thesemeans to discharge regenerated catalyst means to avoid catalysts fromcatalyst short-cutting from the openings in the partition to thedischarge opening are preferably present. Preferably such means are ashield spaced above the catalyst outlet opening in the fast-fluidisedbed zone. A further preferred manner of discharging the generatedcatalyst is shown in FIG. 4.

[0016] With a vertically extending partition is understood a verticalpartition or a more inclined partition which divides the fluidised bedin two fluidised bed zones when viewed from above. Preferably thepartition is for its main or entire part a vertical partition. Thevertical extending partition in the regenerator according to theinvention can be a flat plate. Optionally, but not preferred, morepartitions can be present resulting in more than two fluidised bed zonesof which at least one is a fast-fluidised bed zone and one is the densephase fluidised bed zone as described above. Preferably the verticalpartition has a tubular design resulting in an annular outer fluidisedbed zone and a circular inner fluidised bed zone. The diameter of thetubular partition may be smaller at its lower end in order toaccommodate for example the fluidisation means of the outer fluidisedbed zone.

[0017] If the partition is of a tubular design the outer fluidised bedzone can be the fast-fluidised bed zone and the inner fluidised bed zoneis then the dense phase fluidised bed zone as shown in FIGS. 2-4. Thisembodiment has the advantage that a favourable bed aspect ratio isachieved for the fast-fluidised bed zone, which is in turn beneficial toachieve axial staging of the gas phase. Axial staging of the gas phaseis in turn advantageous for the efficiency of the regeneratorperformance. More preferably the inner fluidised bed zone is thefast-fluidised bed zone and the outer fluidised bed zone is the densephase fluidised bed zone. The advantages of this embodiment are thatregenerated catalyst can be more easily discharged from the regeneratorvessel and because a premixing of spent catalyst and regeneratedcatalyst, as discharged from the primary cyclone diplegs, can be moreeasily achieved in the dense fluidised bed zone. See also FIG. 5.

[0018] The ratio of the cross-sectional area of the fast and densefluidised bed zone is preferably between 1:5 and 2:1. More preferablyless than 60% of the cross-sectional area of the regenerator vessel isoccupied by the fast-fluidised bed zone. A practical optimum is thatabout 50% of the cross-sectional area of the regenerator vessel isoccupied by the fast-fluidised bed zone. In case the annular spacecomprises the fast-fluidised bed zone, the annular space between thetubular partition and the vessel wall is suitably between 3 and 20% ofthe tubular regenerator vessel diameter.

[0019] The openings in the partition should be small enough to avoid amassive flow of oxygenate gas flow from the fast-fluidised bed zone tothe dense fluidised bed zone. These openings should also be large enoughto permit a free flow of catalyst from the dense fluidised bed zone tothe fast-fluidised bed zone. The total area of the openings will dependon the amount of catalyst to be regenerated. Assuming that the totalcatalyst flux through the sum of all openings is between 750 and 1500kg/m².s it is possible to calculate the required area of said openings.

[0020] The openings are preferably evenly spaced along the partition toensure that the fast-fluidised bed zone is provided along its entirebase with catalyst to be regenerated. For example in case of a tubularpartition the openings are suitably provided along its entirecircumference. The resulting evenly and trouble-free distribution ofcatalyst combined with the small bed aspect ratio of the fast-fluidisedbed is advantageous because it limits the chances of after burning.

[0021] The partition may be open at its upper end such that the denseand fast-fluidised bed zones are in open communication with the upperend of the regenerator vessel. Preferably the openings in the partitionare then positioned at the lower end of the partition. Part of therelatively hot catalyst particles present in the upper end of theregenerator vessel can then enter the dense fluidised bed zone fromabove resulting in a temperature rise in this bed, which is advantageousfor regenerator efficiency. The catalyst particles present in the upperend of the regenerator vessel are entrained catalyst particles from thefast-fluidised bed. Part of these catalyst particles will have beenseparated from the gases leaving the regenerator in the means toseparate entrained catalyst from the combustion gases.

[0022] In case the inner fluidised bed zone is the dense fluidised bedzone the vertical partition may also be closed at its upper end suchthat said dense fluidised bed zone is not in open communication with theupper end of the regenerator vessel. In this embodiment the openings inthe partition can be advantageously positioned at an elevated positionin the vertical partition. The higher position is preferred because lessshort-cutting as described above will occur.

[0023] The present invention is also directed to a process forregeneration of spent catalyst in a regenerator vessel, wherein (a)spent catalyst is supplied to a dense fluidised bed present in aregenerator vessel, (b) supplied from the dense fluidised bed to afast-fluidised bed present in the regenerator vessel, (c) contacted withan oxygenate gas as fluidising medium in the fast-fluidised bed at acatalyst density of between 50 and 400 kg/m³, and (d) obtainingregenerated catalyst from the lower end of the fast-fluidised bed.Preferably the catalyst is a spent catalyst of a fluidised catalyticcracking (FCC) process. Preferably such a process is performed in aregenerator vessel as described above.

[0024] With spent catalyst is meant catalyst, which has been used tocrack hydrocarbons in a fluid catalytic cracking (FCC) process and whichhas been stripped, with for example steam, to remove hydrocarbons fromthe catalyst. The remaining so-called spent catalyst will contain coke,which is removed in the regenerator according to the present invention.

[0025] The oxygenate gas used in the fast-fluidised bed is a gascomprising an oxygenate, preferably oxygen. A preferred gas is air orair enriched in oxygen. The gas used in the dense phase fluidised bedcan be an inert gas, for example nitrogen, or recycled combustion gases.Preferably the fluidising gas in the dense phase fluidised bed zone isan oxygenate gas. It can also be a mixture of a fuel containing gas andan oxygenate, for example air and dry gas as obtained in the FCCprocess. In this manner the temperature of the catalyst to beregenerated can be further raised before they are discharged to thefast-fluidised bed zone. This last embodiment is preferably used in aregenerator according to the invention wherein the partition is closedat the top. This design reduces the chances of after burning of the drygas in the top of the regenerator and further. More preferably the samegas is used as fluidising gas in the fast-fluidised bed zone and thedense phase fluidised bed zone. The volume ratio of oxygenate gas addedto the dense phase fluidised bed zone and the volume added to thefast-fluidised bed zone is preferably between 1:40 and 1:5 and morepreferably between 1:20 and 1:5.

[0026] The invention is also directed to a method to retrofit anexisting regenerator vessel provided with means to supply catalystparticles, means to supply an oxygenate gas, means to dischargeregenerated catalyst, means to discharge combustion gases from thevessel and means to separate entrained catalyst from the combustiongases, which vessel also comprises, in use, a fluidised bed zone ofcatalyst at its lower end, by adding a partition in the fluidised bedzone in order to arrive at a regenerator vessel as described above.Preferably no or small changes are applied to the means to separateentrained catalyst from the combustion gases.

[0027] The invention will be illustrated by making use of the followingfigures.

[0028]FIG. 1 represents a state of the art bubbling bed regenerator.

[0029]FIG. 2 first embodiment of the regenerator vessel according theinvention.

[0030]FIG. 3 represents a second embodiment of the regenerator vesselaccording the invention.

[0031]FIG. 4 represents a third embodiment of the regenerator vesselaccording to the invention.

[0032]FIG. 5 is a preferred embodiment wherein the fast-fluidised bedzone is located in the inner tubular fluidised bed zone.

[0033]FIG. 1 shows a state of the bubbling bed regenerator vessel (1)provided with means to supply catalyst particles via catalystdistributor (2), means to supply an oxygenate gas via gas ring (3),means to discharge regenerated catalyst via conduit (4), means todischarge combustion gases from the vessel via conduit (5) and means toseparate entrained catalyst from the combustion gases by primary (6) andsecondary (7) cyclones, of which only one set is shown for clarityreasons. At its lower end the vessel (1) also comprises, in use, abubbling fluidised bed zone (8) having an upper bed level (9). Bothprimary cyclone (6) and secondary cyclone (7) are provided with diplegs(10) respectively (11) (partly shown).

[0034]FIG. 2 shows the same vessel as in FIG. 1, but now provided atubular partition (12), which partition (12) is provided with severalopenings (13) along its circumferential. The tubular partition dividesthe fluidised bed zone of the regenerator in a outer fluidised bed zone(14) and an inner fluidised bed zone (15). In this embodiment the outerfluidised bed zone (14) is the fast-fluidised bed zone having anelevated bed level (16). The outer fluidised bed zone (14) is furtherprovided at its lower end (18) with a gas supply ring (17) as means tosupply an oxygenate gas. Above the catalyst inlet opening (19) of theconduit (4) a plate (20) is positioned to prevent catalyst from shortcutting from openings (13) to inlet opening (19). The catalyst inletopening (19) can be as described in WO-A-0050165. The inner fluidisedbed zone (15) is the dense phase fluidised bed having a lower bed level(21) than bed level (16). This bed level (21) is lower than bed level(16) because the partition is in open communication with the upper end(22) of regenerator vessel (1) and because of the less turbulentfluidisation state of fluidised bed zone (15). Bed level (21) can belocated above or below the discharge opening of the vertical supplyconduit (23). The dense phase fluidised bed zone is also provided with ameans to supply catalyst to be regenerated, which can be a verticalsupply conduit (23) provided at its upper end with a catalyst flowdirecting means (24) to direct catalyst to the dense phase fluidised bedzone (15). Also a gas ring (25) is present to supply a fluidising gas todense phase fluidised bed zone (15).

[0035]FIG. 3 shows a regenerator vessel (1) according to the inventionprovided with a partition (26), which is closed at its upper end (28).The partition encloses a dense phase fluidised bed (27) having a bedlevel (29). The partition is also provided with several openings (30) ata more elevated position than openings (13) of FIG. 2. The tubularpartition walls (26) extend to above the enclosure (28) and to above bedlevel (16) of the fast-fluidised bed zone (14). The extension enclosesan empty space (31), which reduces the volume of the regenerator andimproves the dynamic behaviour of the fast-fluidised bed zone (14). Theextension is provided with an inclined roof (32), which is advantageousto avoid catalyst deposits in the regenerator vessel (1).

[0036]FIG. 4 shows the regenerator according to FIG. 2, wherein theoutlet for regenerated catalyst is provided by a so-called draw-off bin(33), provided with an opening (34) to receive catalyst particles and aconduit (35) to discharge catalyst from the vessel (1). The opening (34)of the draw-off bin (33) is located suitably below the outlet opening ofdipleg (10). The opening (34) of draw-off bin (33) is preferably locatedbelow bed level (16) and suitably in the upper half of thefast-fluidised bed zone (14). The opening (34) is located such that alsocatalyst from fast-fluidised bed zone (14), which has not passed dipleg(10), can enter the draw-off bin (33). By directing the opening (34)up-wards the majority of the catalyst discharged via draw-off bin (33)will advantageously nevertheless be the, sufficiently regenerated,catalyst particles discharged by dipleg (10).

[0037] Preferably one draw-off bin (33) can be positioned between aplurality, preferably 2, of diplegs (10). A typical regenerator cancomprise 8-12 primary cyclones (6), which in turn may be coupled asdescribed above to 4-6 draw-off bins (33). In such an embodiment it willbe necessary to use non-vertically positioned diplegs (10). Suchso-called kinked diplegs preferably have an angle of 15° or less withthe vertical. Embodiments with only one draw-off bin (33) are howeverpreferred.

[0038]FIG. 5 shows the same vessel as in FIG. 1, but now provided atubular partition (12) having an open upper end, which partition (12) isprovided with several openings (36) along its circumferential. Thetubular partition divides the fluidised bed zone of the regenerator inan outer fluidised bed zone (37) and an inner fluidised bed zone (38).In this embodiment the inner fluidised bed zone (38) is thefast-fluidised bed zone having an elevated bed level (39). The innerfluidised bed zone (38) is further provided at its lower end (40) with agas supply ring (41) as means to supply an oxygenate gas. The innerfluidised bed zone (38) is further provided with a regenerated catalystdraw-off conduit (42) having a catalyst inlet opening (43) located belowbed level (39). The outer fluidised bed zone (37) is the dense phasefluidised bed having a significantly lower bed level (44) than bed level(39). To the outer fluidised bed zone (37) spent catalyst is suppliedvia spent catalyst supply conduit (45). This centrally located conduit(45) ends at its upper end into a plurality of diverting arms (46)having a discharge opening (47) located above the outer fluidised bedzone (37). Preferably 2-8, and more preferably four or five arms (46)are present such to evenly discharge the spent catalyst. The fluidisedbed zone (37) is further provided with a gas ring (48) to supply afluidising gas to said dense phase fluidised bed zone.

[0039] In use the regenerator of FIG. 5 will receive spent catalyst via(45). This spent catalyst will be discharged into the dense phasefluidised bed zone (37) and preheated when mixed with hot regeneratedcatalyst being discharged from diplegs (10) and (11). This mixture ofspent and regenerated catalyst will enter the fast fluidised bed zone(38) via openings (36). In this fast fluidised bed zone (38) thecatalyst will move upwardly wherein the majority of the coke present onthe catalyst is combusted. Part of the rising catalyst will bedischarged via draw-off conduit (42) while the remaining part will enterthe regenerator freeboard. Here the catalyst and gas will enter theprimary cyclones (6). Separated catalyst is subsequently discharged viadiplegs (10) and (11) to the dense phase fluidised bed (37) as statedabove.

1. Regenerator vessel provided with means to supply catalyst particles,means to supply an oxygenate gas, means to discharge regeneratedcatalyst, means to discharge combustion gases from the vessel and meansto separate entrained catalyst from the combustion gases, which vesselalso comprises, in use, a fluidised bed zone of catalyst at its lowerend, wherein in the fluidised bed zone a vertically extending partition,which partition is provided with one or more openings, is presentdividing the fluidised bed zone in a dense phase fluidised bed zone anda fast-fluidised bed zone, the dense phase fluidised bed zone providedwith the means to supply catalysts and the fast-fluidised bed zoneprovided with the means to supply an oxygenate gas at its lower end. 2.Regenerator according to claim 1, wherein the vertical partition has atubular design resulting in an annular outer fluidised bed zone and acircular inner fluidised bed zone.
 3. Regenerator according to claim 2,wherein the inner fluidised bed zone is the dense phase fluidised bedzone and the annular outer fluidised bed zone is the fast-fluidised bedzone.
 4. Regenerator vessel according to claim 3, wherein the verticalpartition is closed at its upper end such that the dense fluidised bedzone is not in open communication with the upper end of the regeneratorvessel and wherein the openings in the partition are positioned at anelevated position in the vertical partition.
 5. Regenerator according toclaim 2, wherein the annular outer fluidised bed zone is the dense phasefluidised bed zone and the inner fluidised bed zone is thefast-fluidised bed zone.
 6. Process for regeneration of spent catalystin a regenerator vessel, wherein (a) spent catalyst is supplied to adense fluidised bed present in the regenerator vessel, (b) supplied fromthe dense fluidised bed to a fast-fluidised bed present in theregenerator vessel, (c) contacted with an oxygenate gas as fluidisingmedium in the fast dilute fluidised bed at a catalyst density of between50 and 400 kg/m³, and (d) obtaining regenerated catalyst from the moredilute fluidised bed, wherein part of the regenerated catalyst isdischarged from the regenerator vessel and part is recycled to the densefluidised bed.
 7. Process according to claim 6, wherein the process isperformed in a regenerator vessel according to any one of claims 1-5. 8.Method to retrofit an existing regenerator vessel provided with means tosupply catalyst particles, means to supply an oxygenate gas, means todischarge regenerated catalyst, means to discharge combustion gases fromthe vessel and means to separate entrained catalyst from the combustiongases, which vessel also comprises, in use, a fluidised bed zone ofcatalyst at its lower end, by adding a partition in the fluidised bedzone in order to arrive at a regenerator vessel according to any one ofclaims 1-5.